Piston



R. E. SYKES sept.l 17, 1957 PIsToN l Filed Dec. s. 1954 United States Patent C PIsToN Robert E. Sykes, Evanston, Ill., assignor to Bell & Gossett Company, Morton Grove, lll., a corporation of Illinois Application December 3, 1954, Serial No. 472,874

2 Claims. (Cl. 309-15) My invention relates to pistons and is concerned more particularly with a design thereof which is reflected in certain production and operating advantages.

One object of the invention is to provide a piston constructed and arranged so that it, including the wearing skirt thereof, may be formed as a true, unbroken cylinder, free of any internal ribs or tins, bearing bosses and struts which exercise a control on the expansion of the skirt.

A further object is to provide a piston of the character indicated in which the wearing skirt is composed of a different material from that of the main body of the piston and, specically, one having a substantially lower, heat expansion coeilicient than that of such body.

A further object is the provision of a piston as above set forth in which the main body is composed of aluminum or a material having a relatively high coefficient of expansion and a Wearing skirt composed of a material having a relatively low coetiicient of expansion and which does not 'require any lubrication, such as a graphitic or carbon compound.

These and further objects of the invention will be set forth in the following specication, reference being had tol the accompanying drawing, and the novel means by which the objects are ettectuated will be definitely pointed out in the claims.

In the drawings:

Fig. 1 is a sectional elevation of the piston.

Fig. 2 is a section along the line 2 2 in Fig. 1.

The particular design described herein is more particularly intended for use with small size air compressors such as those which may be driven by M1. to 5% horsepower motors, but the invention is considered to have general application.

Referring to the drawing, the numeral designates the improved piston which is of the trunk type and includes the usual head 11 and a piston ring groove 12 which is intended to be representative of any number of such grooves. Depending from the head 11 is an annular skirt 13 whose outer, cylindrical surface is finished in the conventional manner to an outside diameter substantially less than the usual wearing skirt of the customary piston. Fitting around the annular skirt 13 with a measure of looseness as presently defined is a sleeve whose outer diameter is such as to constitute a wearing skirt 14 for the piston which coacts with a cylinder wall (not shown) in the usual manner. With the wearing skirt 14 in position on the annular skirt 13, these parts are held relative to each other in any approved manner so that aligned ICC holes 15 and 16 may be drilled in the skirts 14 and 13, respectively, in one operation to receive a piston pin 17 Whose ends have a press t in the holes to thereby maintain the axial and circumferential relation of the skirts.

Preferably, the piston components including the head 11 and annular skirt are composed of a material having a substantially higher heat expansion coeicient than that of the material composing the Wearing skirt 14. Accordingly, the outside diameter of the wearing skirt may be sized for a working t with the associated cylinder wall throughout the temperature range to which it may be subjected. Further, the outside and inside diameters of the skirts are sized so that the former substantially takes up the cold clearance between these parts under operating conditions to provide adequate support for the wearing skirt 14. Due to the independent relation of the skirts 13 and 14 to the piston pin 17, the skirts may expand and contract along this pin independently of each other without any interfering stresses.

In one installation that worked satisfactorily for air compressor operation, the piston components 11 and 13 were composed of No. 17 ST. 4 aluminum, while the wearing skirt 14 was composed of U. S. Graphite No. 39. The outside diameter of the skirt 13 Varied from a maximum of 1.968 for use with a minimum inside diameter of the skirt 14 of 1.9715 to a minimum outside diameter of the skirt 13 of 1.967 for use with a maximum inside diameter of the skirt 14 of 1.9725, corresponding, respectively, to annular cold clearances of .0035 and .0055", or an average of .0045.

I claim:

1. A trunk piston having a head, a depending annular skirt, a cylindrical wearing skirt surrounding and coextensive with the annular skirt, the annular skirt and head being composed of a material having a higher heat coefficient of expansion than the material of the wearing skirt and there being a cold clearance of such a value between the opposed lateral surfaces of the annular and wearing skirts that under operating conditions the annular skirt expands to supportably contact the Wearing skirt against lateral pressure, and a piston pin having a press fit in diametrically related holes in both skirts.

2. A trunk piston having an aluminum head, a depending, aluminum, annular skirt, a cylindrical wearing skirt composed of a graphitic compound surrounding and coextensive with the annular skirt, there being a cold clearance of such value between the opposed lateral surfaces of the annular and wearing skirts that under operating conditions the annular skirt expands to supportably contact the wearing skirt against lateral pressure, and a piston pin having a press tit in diametrically related holes in both skirts.

References Cited in the tile of this patent UNITED STATES PATENTS 1,356,695 Chase Oct. 26, 1920 1,929,831 Teetor Oct. l0, 1933 2,123,181 Deputy July 12, 1938 2,221,966 Elder Nov. 19, 1940 2,419,192 Anderson Apr. 22, 1947 2,557,497 Carney June 19, 1951 

